What Is Any Transport Over MPLS (atom)?

Any Transport over MPLS (AToM), also known as Layer 2 VPN (L2VPN), is a technology developed to extend Layer 2 services over an MPLS network. It allows the transport of various Layer 2 protocols and frames across an MPLS backbone, enabling different types of Layer 2 networks to interconnect through MPLS infrastructure. Here's a breakdown of AToM:

Key Concepts of AToM

1. Layer 2 Connectivity:

   • AToM provides a way to transport Layer 2 traffic (such as Ethernet, Frame Relay, ATM) over an MPLS network, which is fundamentally a Layer 3 (IP/MPLS) network. This means that traditional Layer 2 services can operate over an MPLS backbone as if they were on a native Layer 2 network.

2. Encapsulation:

   • Layer 2 frames are encapsulated in MPLS packets. This encapsulation includes adding MPLS labels to the original Layer 2 frames so that they can be transported through the MPLS network and then decapsulated at the destination.

3. Virtual Circuit Emulation:

   • AToM creates virtual circuits between endpoints in the MPLS network. These virtual circuits emulate a direct Layer 2 link between two locations, providing the same behavior as if the devices were directly connected by a Layer 2 link.

How AToM Works

1. Configuration:

   • Service providers configure AToM on their MPLS routers to establish and maintain Layer 2 VPNs. Each Layer 2 service (e.g., Ethernet, Frame Relay) is mapped to an MPLS label that encapsulates the traffic.

2. Label Switching:

   • As Layer 2 frames enter the MPLS network, they are encapsulated with MPLS labels. MPLS routers (Label Switching Routers, LSRs) then forward these labeled packets based on the MPLS labels, rather than inspecting the Layer 2 headers.

3. End-to-End Connectivity:

   • At the egress of the MPLS network, the MPLS label is removed, and the original Layer 2 frame is delivered to the intended destination.

Use Cases for AToM

1. Service Provider Networks:

   • Service providers use AToM to offer Layer 2 VPN services to customers. This allows customers to maintain their existing Layer 2 protocols and services while leveraging the provider's MPLS network for transport.

2. Network Interconnects:

   • AToM is useful for connecting different geographic locations over an MPLS backbone, making it possible to extend private networks across large distances while maintaining Layer 2 functionality.

3. Migration and Integration:

   • AToM facilitates the migration of Layer 2 services to an MPLS infrastructure, enabling seamless integration of legacy Layer 2 networks with modern MPLS networks.

Types of Layer 2 Services Supported

• Ethernet:

  • Ethernet AToM provides transparent LAN services over MPLS.

• Frame Relay:

  • Frame Relay AToM allows Frame Relay networks to be extended over MPLS.

• ATM:

  • ATM AToM enables ATM services to be transported over MPLS networks.

AToM provides a versatile and efficient way to transport a wide variety of Layer 2 services over an MPLS network, simplifying network design and extending service reach.